1. Field of the Invention
The present invention relates to an engine a diagnostic device for an exhaust gas recirculation (EGR) device.
2. Description of the Related Art
There is known an internal combustion engine which has the engine exhaust passage and engine intake passage connected by an exhaust gas recirculation passage and has an exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage. In such an internal combustion engine, usually when the engine cooling water temperature rises above a certain temperature, the exhaust gas recirculation gas is started to be supplied into the intake passage and the amount of the exhaust gas recirculation gas supplied is controlled by the exhaust gas recirculation control valve. In this case, when the exhaust gas recirculation control valve malfunctions and exhaust gas recirculation gas is supplied when it should not be supplied, the combustion efficiency deteriorates. Therefore, it has become necessary to discover at an early period if exhaust gas recirculation gas is being supplied when it should not.
Usually, however, as mentioned above, when the engine cooling water temperature rises above a certain temperature, the exhaust gas recirculation gas starts to be supplied, but at this time the exhaust gas recirculation gas is not continuously supplied. The supply of the exhaust gas recirculation gas is stopped under certain operating conditions. At this time, if the supply of the exhaust gas recirculation gas is completely stopped, then temperature in the exhaust gas recirculation passage falls, but at this time so long as the exhaust gas recirculation gas continues to flow in the exhaust gas recirculation passage, the temperature in the exhaust gas recirculation passage rises. Further, the temperature in the exhaust gas recirculation passage when the supply of the exhaust gas recirculation gas is completely stopped and the temperature in the exhaust gas recirculation passage when exhaust gas recirculation gas flows despite the supply of the exhaust gas recirculation gas supposed to have been stopped change in accordance with the operating state of the engine at that time, for example, the engine load at that time, once the engine cooling water temperature etc. becomes constant such as after completion of engine warm-up.
There is known an internal combustion engine which judges if the exhaust gas recirculation control valve has malfunctioned by judging if exhaust gas recirculation gas continues to flow when the temperature inside the exhaust gas recirculation passage is higher than a set temperature determined by the operating state of the engine when under a specific operating state after completion of engine warm-up when the supply of the exhaust gas recirculation gas should be stopped (Japanese Unexamined Patent Publication No. 3-138444).
However, the temperature in the exhaust gas recirculation passage when the supply of the exhaust gas recirculation gas is stopped and the temperature in the exhaust gas recirculation passage when exhaust gas recirculation gas flows despite the supply of the exhaust gas recirculation gas supposed to have been stopped are more strongly influenced by the past engine operating state before the supply of the exhaust gas recirculation gas was to be stopped than the engine operating state when the supply of the exhaust gas recirculation gas is supposed to be stopped. That is, if a high load operation had continued before the supply of the exhaust gas recirculation gas was supposed to be stopped, the temperature inside the exhaust gas recirculation passage when the supply of the exhaust gas recirculation gas was stopped and the temperature inside the exhaust gas recirculation passage when exhaust gas recirculation gas flows despite that supply of the exhaust gas recirculation gas supposedly being stopped both become higher. If a low load operation continued before the supply of the exhaust gas recirculation gas was supposed to be stopped, then the temperature inside the exhaust gas recirculation passage when the supply of the exhaust gas recirculation gas was stopped and the temperature inside the exhaust gas recirculation passage when exhaust gas recirculation gas flows despite that supply of the exhaust gas recirculation gas supposedly being stopped both become lower.
Therefore, the temperature inside the exhaust gas recirculation passage sometimes becomes higher than the set temperature even when the supply of the exhaust gas recirculation gas has been stopped in cases of an operating state where the supply of the exhaust gas recirculation should be stopped following a continuous high load operation. This leads to the mistaken judgement of the exhaust gas recirculation control valve having malfunctioned at this time. On the other hand, the temperature inside the exhaust gas recirculation passage sometimes becomes lower than the set temperature even when exhaust gas recirculation gas flows in the case of an operating state where the supply of exhaust gas recirculation gas should be stopped following a continuous low load operation. This leads to the mistaken judgement of the exhaust gas recirculation control valve not malfunctioning at this time. That is, it is very difficult to judge if an exhaust gas recirculation control device malfunctions when the supply of the exhaust gas recirculation gas is controlled after the completion of engine warm-up.